Air conditioning system and method

ABSTRACT

An air conditioning system particularly for large buildings in which separate streams of chilled liquid and heated liquid are provided from a refrigeration system to produce cooling and heating throughout the building. A booster heater supplies auxillary heat when that is desirable, and heat is discharged from the system through a heat sink, e.g., a cooling tower or towers. The heat sink has a closed liquid cooling circuit with a coil through which a controlled stream of heat-exchange liquid flows from a condenser of the refrigeration system when it is desirable to discharge heat from the system. The heat-exchange liquid from the air-treating units is returned in an interconnected return liquid supply circuit. When desirable, a stream of the return liquid flows through the closed liquidcooling circuit and thence through the chiller circuit to provide precooling of that liquid. The entire system is controlled to provide a heat balance at all times, and auxillary heat is added to the system only when the heat within the system is less than that which is required.

United States Patent [191 McFarlan Primary ExaminerCharles Sukalo Attorney, Agent, or F irm-Curtis, Morris & Safford Dec. 10, 1974 AIR CONDITIONING SYSTEM AND ings in which separate streams of chilled liquid and METHOD heated liquid are provided from a refrigeration system [76} Inventor: Alden Irving McFarlan, 691 Dorian F produce coolmg and heimng tl 1r oughout the'bufld' Rd westfield NJ 07090 tug. A booster heater supplies auxillary heat when that lS desirable, and heat 15 discharged from the system [22] Filed: Nov. '13, 1972 through a heat sink, e.g., a cooling tower or towers.

- The heat sink has a closed liquid cooling circuit with a [21] Appl' 3053.44 coil through which a controlled stream of heati exchange liquid flows from a condenser of the refrig- [52] US. Cl. 165/22, 165/62 eration system when it is desirable to discharge heat [51] Int. Cl F24f 3/00 from the system. The heat-exchange liquid from the [58] Field of Search 165/1, 2, 22, 50, 26, 27, air-treating units is returned in an interconnected re- 165/62, 63 turn liquid supply circuit. When desirable, a stream of the return liquid flows through the closed liquid- [56] References Cited cooling circuit and thence through the chiller circuit UNITED STATES PATENTS to provide precooling of that liquid. The entire system 2,930,593 3/1960 Blum 165/22 is cmtroned to Provide a heat baiance at all times and auxiliary heat is added to the system only when the heat within the system is less than that which is required.

23 Claims, 3 Drawing Figures PATENTEU U53 I 01974 SHEEI 30F 3 ea 3 r 50 b v f BI HEAT EXCHANGER Fig.3

. 1 AIR CONDITIONING SYSTEM AND METHOD This invention relates to air conditioning, and particularly to such systems which involve utilization of condenser heat.

An object of this invention is to provide improved air conditioning systems and methods. A'further object is to improve the arrangement for controlling the discharge of excess heat from heat-pump air conditioning systems. A further object is to obtain improved efficiency and accuracy in providing a continuous heat balance in air conditioning systems. These and other objects will be in part obvious and in part pointed out below.

In the drawings, each of the figures is a schematic representation of one embodiment of the invention.

Referring to FIG. 1, an air conditioning system 2 has a central station at which there are two refrigeration units 4 and 6. Each of these refrigeration units has the following identical components each of which is identified by a suffix number corresponding to its number: an

evaporator-chiller 8, a compressor 10, a condenser 12, an expansion valve 14, and other standard components and controls which are not shown. A cooling tower 16 provides a very satisfactory heat sink for the system, and has acoil 20, a water spray unit 22, and a blower (not shown). A heat-exchange liquid, i.e., a waterglycol solution, is circulated through coil 20 from a line 23 to a discharge line 24 in which there is a pump 26 and a control thermostat 25. During overall coolingload operation, the heat-exchange liquid flows through the closed circuit of tower 16 and is cooled by evaporative cooling, thereby to discharge the condenser heat from condensers l2-4 and 12-6.

System 2 is of the Three Pipe Envelope type with a plurality of air-treating units, of which units 32 and are illustrative. ln a three-pipe system separate streams of chilled liquid and heated liquid are supplied from a central station to various air-treating units so that each unit receives either all chilled liquid or heated liquid or a mixture of the two, and a single stream of return liquid flows from each of the units. The various streams of return liquid are interconnected or joined so as to provide a common source as make-up liquid for the streams of chilled liquid and heated liquid. In the illustrative embodiment, the return liquid can be mixed with either chilled liquid or heated liquid or it can be used-as either the heated liquid or the chilled liquid. For that mode of operation, the flow paths are such that the system exhibits a preference for supplying the heated liquid circuit with return liquid from one or more of the air-treating units, and for supplying the chilled liquid circuit with return liquid fromanother unit or units.

Unit 32 receives fresh air at inlet 34 and return air at inlet 36, and suppplies conditioned interior air at outlet 38 for interior zones of thebuilding, i.e., the peripheral rooms and the core of the building. Unit 40 re-' ceives return air at inlet 42, and supplies conditioned air at outlet 44 for the various zones of the periphrey or envelope of the building, and handles only the heating and cooling loads caused by conduction through the exterior walls of the building. Units 32 and 40 receive hot or heated liquid from line 46, chilled liquid from line 48 andreturn liquid from line 67. The common return line is formed by lines 50 and 52 extending from units 32and 40, respectively, a pair of pumps 54 and 56 which discharge lines 58 and 60, respectively, a line 62 connecting lines 50 and 52, and a line 64 connecting lines 58 and 60. A line 66 which is in general alignment with line 58 carries the stream of liquid which eventually flows to chilled liquid line 48, and extends from line 64 to chillers 8-6 and 8-4 in series, and a line 68 which is in general alignment with line 60 and extends from line 64 to condensers 12-4 to discharge it to line 60 and to line 68 for the chilled liquid line. But line 62 permits cross-flow between lines 50 and 52 so that either pump can draw return liquid from either of lines 50 or 52, and line 64 permits crossflow between lines 58 and 60 so that either pump can discharge liquid through either of lines 66 or 68. Return liquid line 67 is connected to line 64 and permits the recirculation of the return liquid from either of pumps 54 or 56. Return liquid line 67 and heated liquid line 46 extends to two three-way mixing valves 61 and 65, which have discharge lines 63 and 69, respectively, extending to three-way mixing valves 81 and 85 which control the flow of liquid to the air-treating units 32 and 40, respectively. Chilled liquid line 48 also extends to valves 81 and 85, and those valves are controlled thermostatically in response to the temperature of the air discharged from their respective units. Under that control valve arrangement, either heated liquid or return liquid or a mixture of the two, is supplied from valve 61 through line 63 to valve 81, and either chilled liquid or the liquid from line 63, or a mixture of the two, is supplied to coil 83 of unit 32 to maintain the desired temperature for the air discharged from unit 32 at 38. Similarly, valve 85 supplies coil 89 of unit 40 with liquid from either both of lines 69 and 48 to maintain the desired temperature of the air which is discharged at 44 from unit 40. With each of units 32 and 40, the liquid is solely chilled liquid, or solely heated liquid, or solely return liquid, or it may be a mixture of any two or all of them. As indicated above, cooling tower 16 acts as a heat-sink for the system when there is an excess of heat in the system. With that operating condition, coil 20 of the cooling tower receives liquid to be cooled from the condenser discharge line through a line 80, a three-way mixing valve 82, a line 84, a three-way mixing valve 86 and line 23. The liquid flows from coil 20 through line 24 and pump 26 to discharge line 88 which extends to line 68 at the inlet side of condenser 12-4. Line 88 also extends to valve 82 so that liquid which is discharged from coil 20 may be recirculated through the coil. Hence, valve 82 can be operated to mix the liquid from the tower with a stream of the heated liquid from line so as to reduce the temperature of the liquid flowing through coil 20. That reduction in the liquid temperature causes a reduction in the amount of heat discharged from the system through the cooling tower and gives precise control. That constitutes a means for providing precise control of the amount of heat discharged from the system.

A line 92 extends from the return liquid line 67 to mixing valve 86 so that return liquid can be mixed with the liquid from condenser 12-6 through line 84, or return liquid only can be supplied to coil 20. Line 88 also extends to a three-way mixing valve 90 in line 66 through which liquid is supplied to the chilled water circuit. Hence, for some conditions of operation a stream of return liquid is directed through line 92 and valve 86 to the cooling tower and a corresponding stream is supplied through line 88 and valve 90 to line 66. That pre-cools the liquid flowing to the chilled liquid circuit, thus providing free-cooling, for example, when the refrigeration units are not operating. Valves 86 and 90 are interconnected so that they move together, with valve 86 supplying the same portion of return liquid to the cooling tower as valve 90 delivers to line 66. The remainder of the liquid flowing directly to the cooling circuit through valve 90 is return liquid.

It is thus seen that the cooling tower acts as a variable I heat-sink and can receive 100 percent heated liquid for maximum discharge of heat, and that the rate at which heat is discharged can be reduced further by recirculating some of the liquid so that the amount of heated liquid from line 70 may be gradually reduced to zero. A still lesser amount of heat is discharged by pre-cooling a stream of return liquid and supplying it to the chilled liquid line. Hence, the rate at which heat is discharged is varied with accurate control throughout the entire range.

The break-even temperature for a system is that temperature at which the internally created heat exactly balances the heat losses from the system. At temperatures within the range directly above the break-even temperature, it is desirable to provide relatively high temperature heated liquid for the air-treating units which handle the heating loads. That is provided with the present system as a result of the fact that (at that time) a substantial portion of the liquid flowing through coil of the cooling tower is recirculated liquid from line 88 and there is a relatively small amount of heated liquid flowing through line 80 to the tower and a corresponding reduction in the stream of heated liquid flowing through the condensers. Accordingly, all of the condenser heat must be absorbed by that relatively small stream of the liquid flowing to the air-treating units. That raises the temperature level within the condensers so that the temperature of the heated liquid is raised to a level which insures a proper heat transfer in the peripheral air-treating units.

The two pumps 54 and 56 act in parallel as components of the basic three pipe system. The addition of pump 26 and its associated liquid lines and valves provide the widely varying range of liquid flow conditions to insure the proper discharge of heat from the system at all times.

The air conditioning systems of FIGS. 2 and 3 are similar-"to thatof FIG. 1, and identical components are numbered the same. Referring to FIG. 2, an aincbnditioning system has a central station with two refrigeration units 4 'and 6, and there are identical components each of which is identified by a suffix number corresponding to the number of its unit: an evaporatorchiller 8, a compressor 10, a condenser 12, an expansion valve 14, two cooling towers 16 and 18 which provide the heat sink for the system. Cooling tower 18 is an open evaporative tower for condenser 12-6, and a pump 28 circulates cooling water from the sump of tower 18 through a line 29 to condenser 12-6 and thence through a line 30 back to tower 18. Line 66 is in general alignment with line 58 and extends from line 64 to chillers 8-4 and in series to the chilled liquid line 48. The stream of return liquid to be heated passes through condenser 12-4 and thence through line 70, a three-way mixing valve 76 and booster heater 72 to the hot liquid line v46. The return liquid line 67 is connected to valve 76, so that valve 76 can pass hot liquid from condenser 12-4 to line 46, or that valve can be turned to bypass the condenser so that all or part of the liquid flowing to hot liquid line 46 is return liquid flowing from line 67. 1

Cooling tower 16 cools liquid from condenser 12-4 with the liquid flowing through a liquid cooling circuit formed from line through line 104, a three-way valve 106, a line 109, a three-way valve 108, line 23, coil 20, line 24, pump 26, a three-way valve 110, and a line 112 which extends to line 68 and thence back to the condenser. That circulation is produced by the operation of pump 26 when valves 106, 108 and 110 are positioned to providethat flow. A line 114 connects line 112 to valve 106, and valve 106 is adapted to mix the heated liquid from line 104 with the liquid returning from the tower through line 114, so that a controlled portion of heated liquid flows to the tower and the remainder of the stream is recirculated liquid from line 114. That recirculated liquid portion may be varied from zero to percent, and the temperature of the composite stream is varied accordingly, as in FIG. 1. That provides a very satisfactory control upon the amount of heat discharged from the system, and also provides a control for the temperature of the heated liquid flowing to the heated liquid line 46. Cooling tower 16 is also used to provide pre-cooling for return liquid flowing to the chilled liquid circuit, there being a line 116 extending from the return liquid line 67 to valve 108, and a line 118 extending from valve to line 66. For that mode of operation, valve 108 is positioned so as to close its circuit from line 109 and only recirculated liquid from line 67 can flow through line 116 to valve 108. Hence, valve 108 supplies a controlled portion or return liquid from line 116, and the valves 108 and 110 are interconnected so that they are moved together, and act in the manner of valves 86 and 90 in FIG. 1. The amount of precooled liquid supplied to chiller 8-6 is controlled by valves 108 and 110, which also provide the desired recirculation of liquid through lines 112, 114 and 109 as in FIG. 1.

In accordance with the present invention, the master controller acts at all times to discharge heat at the rate required to balance the addition of heat to the system. .In addition to the controls discussed above, cooling tower 16, can be operated dry" (i.e., without the water spray) so that it discharges a reduced amount of heat, solely by conduction with the air.

The present inventidncontemplates that it is not necessary to vary 'the amount of air throughout the normal range of operation.- Hence, the quantity of outside air supplied is that required for ventilation only, and it is not necessary to supply additional air solely for the purpose of carrying away heat. The present invention utilizes the simple standard type of condensers to perform two separate functions, namely, to provide a stream of heated liquid for the air-treating units and to discharge heat from the system through cooling tower 16 when that is desirable. The system operates throughout wide ranges of heating and cooling load conditions to maintain the desired heat balance with uninterupted satisfactory performance.

In the system of FIG. 3 the cooling tower of FIG. 1 is replaced by a liquid-to-liquid heat exchanger 118 in which water from a well 120 is used as the heat sink and is returned to the ground at 122. A stream of liquid for the chilled liquid circuit is supplied through a valve 124 and a line 126, and is made up of either return liquid from line 128 or heated liquid from line 70 through a line 130, or a mixture of the two. The liquid from line 126 flows through heat exchanger 118 counter-current to the well water, and flows through a line 132 to evaporator-chiller 8-6 and thence through chiller 8-4 to chilled liquid line 48.

The well water provides a heat sink of substantially constant temperature so that relatively low tempera ture liquid is provided in line 132. The booster heater 72 has a bypass line 134 which extends to a valve 136 and which delivers liquid from the booster heater or directly from condenser 12-6, or a mixture of the two, to the heated liquid line 46. The system of FIG. 3 is otherwise the same as in FIG. 1 and the operations are similar. The liquid from heat-exchanger 118 always flows to the chilledliquid circuit. Where feasible, well water can be used as the heat-exchange liquid throughout the system, thus, making the heat-exchanger 118 unnecessary. It is also understood that the water may be provided from other sources where feasible.

In each of the systems of FIGS. 1, 2 and 3 the quantity of air supplied to the conditioned space or zones remains constant throughout the year. That differs from the prior practice of utilizing a variable quantity of outside air as a cooling medium when the outside temperature and the operating conditions make that desirable. With those systems, the volume of outside air is varied from the minimum required for ventilation at very low temperatures and high temperatures to a condition at intermediate temperatures in which all of the return air is discharged and 100 percent outside air is brought into the system. It is generally considered that the minimum amount of outside air required for ventilation is of the order of 25 percent of the total air supplied to the various zones. Hence, with those prior systems ithas not been uncommon to increase the total quantity of air to four times that required for ventilation. Such excess air must be filtered and it must be dehumidified if its humidity is above the acceptable level.

1 is substantial additional cost for such equipment and for its maintenance and operation. Also, for high humidity outside air conditions, a substantial refrigeration load is created by bringing in the additional quantity of outside air for cooling, and the dehumidified air is then discharged.

The present invention provides systems from which heat is discharged to provide an accurately controlled heat balance over wide ranges of operating conditions. Each zone is provided with the amount of outside air which it requires and the outside fan and duct assembly is simplified accordingly. Requirements for variations in the quantity of outside air can be complied with without departing from the spirit of the invention.

What is claimed is:

1. In an air conditioning system having a plurality of zones, the combination of, means to supply a substantially uniform stream of outside air to said system, refrigeration means having a chiller in which one stream of heat-exchange liquid is cooled to provide a stream of chilled liquid and also having condenser means in which a stream of the heat-exchange liquid is heated to provide a stream of heated liquid, air-treating means to pass streams of air which includes said stream of outside air to said zones in heat-exchange relationship with controlled portions of said streams of chilled liquid and heated liquid, means to pass the liquid from said airtreating means to said refrigeration means as return liquid, heat-sink means having a liquid flow path along which liquid flows in heat-exchange relationship with a heat absorbing fluid, means to pass along said liquidfluid flow path a stream of liquid which comprises all or part of said stream of said heated liquid or part of said return liquid or a mixture of the two, and control means which is responsive to the requirements for heating and cooling in said zones and which acts to regulate the portion of said stream of heated liquid flowing along said liquid flow path of said heat-sink means.

2. A system as described in claim 1 wherein said airtreating means comprises a plurality of independently operating air-treating units through which air is supplied to said zones, and wherein controlled portions of said streams of heated liquid and chilled liquid are delivered to each of said air-treating units, and wherein return liquid from said units provides the liquid for said streams of heated liquid and chilled liquid, and means to pass a portion of said return liquid along said liquid flow path of said heat-sink means and thence through said chiller to said chilled liquid stream whereby a portion of the return liquid is cooled in said heat-sink 1 means and then isfurther cooled by said chiller.

3. A system as described in claim 1 wherein said heatsink means comprises a liquid coil in which the stream of liquid passes in heat-exchange relationship with a stream of air.

4. The system as described in claim 1 which includes means operable to add heat to the system, and wherein said control means includes means to exert control over the operation of the entire system to discharge heat from the system through said heat-sink means when there is excess heat in the system and to add heat to the system when there is a deficiency of heat in the system. I

5. An air conditioning system as described in claim 4 which includes pump means in the flow circuit for liquid passing through said heat-sink means, bypass means to divert liquid from the discharge side of said flow path back to the entry side of said flow path, and liquid flow control means to mix recirculated liquid from said bypass means with liquid flowing from said stream of heated liquidto thereby regulate the temperature of liquid flowing through said heat-sink means in response to the need to control the rate at which heat is discharged through said heat-sink means and thereby provide only the amount of heat required to satisfy the deficiency in the system.

6. An air conditioning .system as described in claim 5 wherein said control means exerts overall control on the system in response to the temperature of said stream of heated liquid.

7. An air conditioningsystem as described in claim 1 wherein the liquid returning from said air-treating means provides a common source for liquid flowing to said stream of heated liquid and said stream of chilled liquid and which may also be returned without a substantial change in its temperature to said air-treating means.

8. An air conditioning system as described in claim 1 wherein said refrigeration means includes a second chiller whereby the stream of chilled liquid is cooled by stages, and wherein said chillers are evaporator chillers of separate refrigeration units, and which includes a cooling tower which provides cooling water for the condenser of one of said refrigeration units.

9. An air conditioning system as described in claim 1 wherein said air-treating units includes one airtreating unit which is supplied with liquid from said stream of chilled liquid and the return liquid.

10. An air conditioning system as described in claim 9 which includes means to deliver a portion of said stream of heated liquid and the-return liquid to one of said air-treating units.

11. An air conditioning system as described in claim 10 wherein said heat-sink means comprises an evaporative cooling tower, and wherein said controlmeans includes means to pass a stream of return liquid through said heat sink means and thence to said stream of chilled liquid.

12. A system as described in claim 1 wherein said I heat-absorbing fluid comprises a stream of external water.

13. A system as described in claim 12 wherein said stream of external water is water from a well.

14. A system as described in claim ll which includes means to pass the entire stream of liquid from said heat-sink means along the path to form said stream of chilled liquid.

15. A system as described in claim 1 which includes means to recirculate liquid along said liquid-flow path by mixing a'portion of such liquid with the liquid supplied from said streams.

16. In an air conditioning system having a plurality of zones, the combination of, means to supply a substantially uniform stream of outside air to said system, refrigeration means including a chiller in which one stream of heat-exchange liquid is cooled to provide a stream of chilled liquid and also having condenser means in which a stream of the heat-exchange liquid is heated to provide a stream of heated liquid, air-treating means to pass streams of air which includes said stream of outside air to said zones in heat-exchange'relationship with controlled portions of said streams of chilled liquid and heated liquid, heat-sink means having a liquid-fluid flow path along which heated liquid flows in heat-exchange relationship with a heat-absorbing fluid, means to pass a portion of said stream of heated liquid along said flow path of said heat-sink means and thence back to said condenser means thereby to deliver heat from said condenser means to said heat-absorbing fluid in said heat-sink means, and control means which is responsive to the requirements for heating and cooling in said zones and which acts to regulate the heat discharged by the portion of said stream of heated liquid flowing to said heat-sink means.

17. A system as described in claim 16 which includes means to mix a portion of the liquid flowing from said heat-sink means with said portion of said stream of heated liquid to thereby reduce the temperature of the liquid flowing along said liquid-flow path.

18. In an air conditioning system, the combination of, refrigeration means having a chiller in which a stream of heat .exchange liquid is cooled to provide a stream of chilled liquid and having condenser means in which a stream of the liquid is heated to provide a stream of heated liquid, heat-sink means having a liquid-fluid flow path along which heated liquid flows in heatexchange relationship with a heat-absorbing fluid, means to pass a portion of said stream of heated liquid along said flow path of said heat-sink means and thence back to said condenser means thereby to deliver heat from said condenser means to said heat-absorbing fluid in said heat-sink means, and control means which regulates the heat discharged by the portion of said stream of heated liquid flowing to said heat-sink means.

19. In an air conditioning system of the character described wherein streams of chilled liquid and heated liquid are supplied to air-treating units from a refrigeration system at a central station and the heat exchange liquid is returned to the central system as return liquid, the combination of, heat-sink means for discharging heat from the system when that is desirable, means to direct a portion of the stream of heated liquid through said heat-sink means in a controlled manner to discharge heat from the system at a desired rate, and means to direct a stream of return liquid through said heat sink means and thence back to the refrigeration unit to provide the liquid for said stream of chilled liquid.

20. The combination as described in claim 19 which includes means to recirculate liquid through said heatsink means in the form of a composite stream of recirculated liquid and a portion of the stream of heated liquid.

21. In an air conditioning system having a plurality of zones, the combination of, refrigeration means having a chiller with a chiller path in which one stream of heatexchange liquid is cooled to provide a stream of chilled liquid and condenser means with a heating path in which a stream of the heat-exchange liquid is heated to provide a stream of heated liquid, air-treating means to pass streams of air to said zones after passing in heatexchange relationship with controlled portions of said streams of chilled liquid and heated liquid, means to pass the liquid as return liquid from said air-treating means to said chiller path and said heating path of said refrigeration means, heat-sink means having a liquidfluid flow path, means to pass a stream of heat-sink liquid along said liquid-fluid flow path, said stream of heat-sink liquid comprising all or part of said stream of said heated liquid or part of said return liquid or a mixture of the two, and control means which is responsive to the requirement for discharging heat from the system and and which acts to regulate the portions of said streams of heated liquid and return liquid flowing to said flow path of said heat-sink means.

22. A system as described in claim 21 which includes means to supply a substantially uniform stream of outside air to said system, and wherein said air-treating means comprises a plurality of independently operating air-treating units through which air is supplied to air zones, and wherein controlled portions of said streams of heated liquid and chilled liquid are delivered to each 23. A system as described in claim 21 wherein a of said air-treating units, and wherein return liquid stream of said liquid flows from said heat-sink means to from said units provides the liquid for said streams of said stream of chiller liquid. heated liquid and chilled liquid. r 

1. In an air conditioning system having a plurality of zones, the combination of, means to supply a substantially uniform stream of outside air to said system, refrigeration means having a chiller in which one stream of heat-exchange liquid is cooled to provide a stream of chilled liquid and also having condenser means in which a stream of the heat-exchange liquid is heated to provide a stream of heated liquid, air-treating means to pass streams of air which includes said stream of outside air to said zones in heat-exchange relationship with controlled portions of said streams of chilled liquid and heated liquid, means to pass the liquid from said air-treating means to said refrigeration means as return liquid, heat-sink means having a Liquid flow path along which liquid flows in heat-exchange relationship with a heat absorbing fluid, means to pass along said liquid-fluid flow path a stream of liquid which comprises all or part of said stream of said heated liquid or part of said return liquid or a mixture of the two, and control means which is responsive to the requirements for heating and cooling in said zones and which acts to regulate the portion of said stream of heated liquid flowing along said liquid flow path of said heat-sink means.
 2. A system as described in claim 1 wherein said air-treating means comprises a plurality of independently operating air-treating units through which air is supplied to said zones, and wherein controlled portions of said streams of heated liquid and chilled liquid are delivered to each of said air-treating units, and wherein return liquid from said units provides the liquid for said streams of heated liquid and chilled liquid, and means to pass a portion of said return liquid along said liquid flow path of said heat-sink means and thence through said chiller to said chilled liquid stream whereby a portion of the return liquid is cooled in said heat-sink means and then is further cooled by said chiller.
 3. A system as described in claim 1 wherein said heat-sink means comprises a liquid coil in which the stream of liquid passes in heat-exchange relationship with a stream of air.
 4. The system as described in claim 1 which includes means operable to add heat to the system, and wherein said control means includes means to exert control over the operation of the entire system to discharge heat from the system through said heat-sink means when there is excess heat in the system and to add heat to the system when there is a deficiency of heat in the system.
 5. An air conditioning system as described in claim 4 which includes pump means in the flow circuit for liquid passing through said heat-sink means, bypass means to divert liquid from the discharge side of said flow path back to the entry side of said flow path, and liquid flow control means to mix recirculated liquid from said bypass means with liquid flowing from said stream of heated liquid to thereby regulate the temperature of liquid flowing through said heat-sink means in response to the need to control the rate at which heat is discharged through said heat-sink means and thereby provide only the amount of heat required to satisfy the deficiency in the system.
 6. An air conditioning system as described in claim 5 wherein said control means exerts overall control on the system in response to the temperature of said stream of heated liquid.
 7. An air conditioning system as described in claim 1 wherein the liquid returning from said air-treating means provides a common source for liquid flowing to said stream of heated liquid and said stream of chilled liquid and which may also be returned without a substantial change in its temperature to said air-treating means.
 8. An air conditioning system as described in claim 1 wherein said refrigeration means includes a second chiller whereby the stream of chilled liquid is cooled by stages, and wherein said chillers are evaporator chillers of separate refrigeration units, and which includes a cooling tower which provides cooling water for the condenser of one of said refrigeration units.
 9. An air conditioning system as described in claim 1 wherein said air-treating units includes one air-treating unit which is supplied with liquid from said stream of chilled liquid and the return liquid.
 10. An air conditioning system as described in claim 9 which includes means to deliver a portion of said stream of heated liquid and the return liquid to one of said air-treating units.
 11. An air conditioning system as described in claim 10 wherein said heat-sink means comprises an evaporative cooling tower, and wherein said control means includes means to pass a stream of return liquid through said heat sink means and thence to said stream of chilled liquid.
 12. A system as described in claim 1 wherein said heat-absorbing fluid comprises a stream of external water.
 13. A system as described in claim 12 wherein said stream of external water is water from a well.
 14. A system as described in claim 11 which includes means to pass the entire stream of liquid from said heat-sink means along the path to form said stream of chilled liquid.
 15. A system as described in claim 1 which includes means to recirculate liquid along said liquid-flow path by mixing a portion of such liquid with the liquid supplied from said streams.
 16. In an air conditioning system having a plurality of zones, the combination of, means to supply a substantially uniform stream of outside air to said system, refrigeration means including a chiller in which one stream of heat-exchange liquid is cooled to provide a stream of chilled liquid and also having condenser means in which a stream of the heat-exchange liquid is heated to provide a stream of heated liquid, air-treating means to pass streams of air which includes said stream of outside air to said zones in heat-exchange relationship with controlled portions of said streams of chilled liquid and heated liquid, heat-sink means having a liquid-fluid flow path along which heated liquid flows in heat-exchange relationship with a heat-absorbing fluid, means to pass a portion of said stream of heated liquid along said flow path of said heat-sink means and thence back to said condenser means thereby to deliver heat from said condenser means to said heat-absorbing fluid in said heat-sink means, and control means which is responsive to the requirements for heating and cooling in said zones and which acts to regulate the heat discharged by the portion of said stream of heated liquid flowing to said heat-sink means.
 17. A system as described in claim 16 which includes means to mix a portion of the liquid flowing from said heat-sink means with said portion of said stream of heated liquid to thereby reduce the temperature of the liquid flowing along said liquid-flow path.
 18. In an air conditioning system, the combination of, refrigeration means having a chiller in which a stream of heat exchange liquid is cooled to provide a stream of chilled liquid and having condenser means in which a stream of the liquid is heated to provide a stream of heated liquid, heat-sink means having a liquid-fluid flow path along which heated liquid flows in heat-exchange relationship with a heat-absorbing fluid, means to pass a portion of said stream of heated liquid along said flow path of said heat-sink means and thence back to said condenser means thereby to deliver heat from said condenser means to said heat-absorbing fluid in said heat-sink means, and control means which regulates the heat discharged by the portion of said stream of heated liquid flowing to said heat-sink means.
 19. In an air conditioning system of the character described wherein streams of chilled liquid and heated liquid are supplied to air-treating units from a refrigeration system at a central station and the heat exchange liquid is returned to the central system as return liquid, the combination of, heat-sink means for discharging heat from the system when that is desirable, means to direct a portion of the stream of heated liquid through said heat-sink means in a controlled manner to discharge heat from the system at a desired rate, and means to direct a stream of return liquid through said heat sink means and thence back to the refrigeration unit to provide the liquid for said stream of chilled liquid.
 20. The combination as described in claim 19 which includes means to recirculate liquid through said heat-sink means in the form of a composite stream of recirculated liquid and a portion of the stream of heated liquid.
 21. In an air conditioning system having a plurality of zones, the combination of, refrigeration means having a chiller with a chiller path in which one stream of heat-exchange liquid is cooled to provide a stream of chilled liquid And condenser means with a heating path in which a stream of the heat-exchange liquid is heated to provide a stream of heated liquid, air-treating means to pass streams of air to said zones after passing in heat-exchange relationship with controlled portions of said streams of chilled liquid and heated liquid, means to pass the liquid as return liquid from said air-treating means to said chiller path and said heating path of said refrigeration means, heat-sink means having a liquid-fluid flow path, means to pass a stream of heat-sink liquid along said liquid-fluid flow path, said stream of heat-sink liquid comprising all or part of said stream of said heated liquid or part of said return liquid or a mixture of the two, and control means which is responsive to the requirement for discharging heat from the system and and which acts to regulate the portions of said streams of heated liquid and return liquid flowing to said flow path of said heat-sink means.
 22. A system as described in claim 21 which includes means to supply a substantially uniform stream of outside air to said system, and wherein said air-treating means comprises a plurality of independently operating air-treating units through which air is supplied to air zones, and wherein controlled portions of said streams of heated liquid and chilled liquid are delivered to each of said air-treating units, and wherein return liquid from said units provides the liquid for said streams of heated liquid and chilled liquid.
 23. A system as described in claim 21 wherein a stream of said liquid flows from said heat-sink means to said stream of chiller liquid. 